JP5614831B2 - Oxide superconducting current lead - Google Patents

Description

  The present invention relates to an oxide superconducting current lead for supplying current from a power source to a cryogenic device using superconductivity, for example, a superconducting magnet, a superconducting cable or a superconducting transformer that requires a large current.

  When operating a superconducting application device, for example, a superconducting magnet, it is necessary to cool the magnet to a cryogenic temperature in order to bring the magnet into a superconducting state. Current leads are required. In this case, it is necessary to suppress the heat intrusion to the cryogenic device as much as possible, but the heat intrusion from the current lead is the largest.

  The current lead needs to be a good conductor, but if a metal such as Cu or Al with low electrical resistance and high thermal conductivity is used, superconductivity will occur due to heat penetration from the outside in addition to Joule heating of the current lead itself. There is a problem that the cooling efficiency of the magnet is deteriorated, and the cooling cost for maintaining the superconducting state is enormous.

In order to solve this problem, it is necessary to achieve both conductivity and low thermal conductivity as the current lead used in the superconducting magnet. Since the superconducting magnet also cools the current lead part, the thermal conductivity is small and Joule heat is generated. By using an oxide superconductor that does not occur as a current lead, it is possible to keep the amount of heat penetration low while supplying current. That is, a current lead using an oxide superconductor is high at a liquid nitrogen temperature. Since the current density can be obtained, it is possible to easily supply a large current to superconducting equipment that requires a large current, and it is possible to reduce the inflow from the outside due to the low conductivity. It is possible to reduce the loss of refrigerant such as liquid helium and improve the cooling efficiency of the refrigerator.

In this case, as a superconductor used for the superconducting current lead, a Bi body such as Bi (2223) or Bi (2212) system and a bulk body of rare earth oxide superconductor represented by YBa ₂ Cu ₃ O _x are used. Silver sheathed wires that have been formed into rods or cylinders, or superconductor parts coated with silver or silver alloys with high critical current density (Jc), have been used, and many superconducting filaments are placed in a silver matrix. A tape-shaped current lead is known (see, for example, Patent Documents 1 and 2).

  On the other hand, as a current lead, a tape-shaped superconducting current lead in which an oxide superconductor and a silver tape are alternately laminated using a tape-shaped superconductor provided with an oxide superconducting layer on a metal substrate is known ( For example, see Patent Document 3.)

  Furthermore, a tape-shaped oxide superconducting wire having an intermediate layer formed on a metal substrate, and an oxide superconducting layer and a stabilizing layer sequentially formed on the intermediate layer is known. The wire has a high critical current value, and the Ni-based alloy substrate normally used as a metal substrate has a thermal conductivity as small as about 1/4 compared to silver or a silver alloy. The mechanical strength of the alloy substrate may be very large, and it is a wire suitable for application to oxide superconducting current leads, and the current obtained by winding such a tape-shaped oxide superconducting wire around the support member Lead is known (for example, refer to Patent Document 4).

JP-A-9-115356 JP-A-5-218513 Japanese Patent Laid-Open No. 5-243044 JP 2008-305765 A

  As described above, various current leads using oxide superconductors are known, but current leads using oxide superconductor bulk bodies are excellent in thermal insulation, but increase in current carrying capacity. Therefore, it is necessary to change the manufacturing process each time, and it is difficult to manufacture a small cross-sectional area or a compact current lead from the viewpoint of the manufacturing process and mechanical strength. There's a problem.

  In addition, current leads using silver alloy sheathed wires can be solved by adjusting the number of wires used to increase or decrease the current carrying capacity, but in order to improve the crystal orientation, rolling is applied. It is necessary to form a tape, and therefore a silver or silver alloy sheath with a certain thickness is required, and the sheath material is silver or a silver alloy having a very high thermal conductivity. The current lead is low compared to the current lead used, and there is a drawback that the thermal conductivity of the current lead itself increases. For this reason, it is essential to reduce the amount of wire used and to make it longer, and it is difficult to make it compact.

  On the other hand, the tape-shaped superconducting current lead in which the oxide superconductor and the silver tape are alternately laminated has a problem that the thermal conductivity of the current lead itself is increased, and the tape-shaped oxide superconducting wire is used as a support member. The current leads wound around the outer periphery use a metal with high thermal conductivity such as silver as the stabilizing material, so it is necessary to increase the length to reduce the amount of heat penetration. Since the wire is wound around the outer periphery of the support member, there is a limit to lengthening the heat intrusion path as described above, and there is a problem that the compactness of the current lead is lost.

  The present invention has been made to solve the above problems, and is easy to manufacture and has a small cross-sectional area, ie, a long heat intrusion path, in order to keep the amount of heat intrusion low. It is an object of the present invention to provide an oxide superconducting current lead capable of reducing the thermal conductivity of the current lead itself.

In order to achieve the above object, the oxide superconducting current lead of the present invention is a current lead for connecting a superconducting device and a power supply source, and the current lead is connected to both sides of the support member. comprising a pair of electrodes and a the two electrodes and electrically connected to the current path, the meandering shape of the current path between the electrodes, the oxide superconducting layer via an intermediate layer was formed on the substrate by the MOD method Each of the connection end portions projecting in the electrode direction at both ends of each current path is formed by a plurality of oxide superconductors having a plurality of oxide superconductors , and each current path is disposed in close contact with or bonded to a flat support member. Is connected to both electrodes .

  The meander shape described above refers to a zigzag, meander or zigzag folded shape used in a transmission path such as a circuit board of an electronic device.

  Further, a current path made of this meander-shaped oxide superconductor is formed by an odd number of straight line portions arranged in parallel and a connection portion for sequentially connecting adjacent end portions of the odd number of straight line portions. You can also.

  The supporting member in the above invention can have any shape such as a flat plate shape, a columnar shape, or a cylindrical shape, but it needs to have a shape that can support a meander-shaped oxide superconductor that is a current path. .

  Further, since the support member needs to have mechanical strength, it is a metal member such as SUS, Cu, Al or Ag alloy, preferably a non-magnetic material such as GFRP, stainless alloy, nickel base alloy or titanium alloy, In addition, it is made of a low thermal conductivity material.

  When the support member is formed of a metal member, electrodes made of oxygen-free copper or the like are electrically connected to both ends of the support member via an electrically insulating material having a low thermal conductivity such as GFRP.

  Both ends of the oxide superconductor having a meander shape formed by the MOD method serving as a current path are electrically connected between both the electrodes by soldering or the like. The oxide superconductor is disposed with its stabilizing layer in close contact with or bonded to the support member, or the oxide superconductor is disposed in close contact with or bonded to the support member. It may be placed on the support member via

The oxide superconductor in the above invention is REBa _x Cu ₃ O _y (RE is Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm) formed on the substrate via an intermediate layer. 1 or 2 or more elements selected from Yb, where x ≦ 2 and y = 6.2 to 7. Hereinafter, referred to as REBCO. A stabilizing layer is coated on top.

  The REBCO-based superconductor can be formed by a pulsed laser (PLD) method, a chemical vapor deposition (CVD) method, a metal organic acid salt or an organic metal compound as a raw material, as long as the area can be increased. The MOD method (Metal Organic Deposition Processes), that is, after applying a raw material solution in which the organic compound of the metal component is uniformly dissolved is applied on the substrate. It is preferably formed by a method of forming a thin film on a substrate by heating and thermally decomposing it.

  Examples of the coating method include a spin coating method, a dip coating method, an ink jet method, and a spray method. However, the coating method is not limited by this example as long as it is a process capable of continuously coating a solution on a substrate. The coating thickness per one time is 0.01 to 3.0 μm, and preferably 0.1 to 1.0 μm.

  In the MOD method, one or more intermediate layers with improved in-plane orientation and orientation are formed on a metal substrate having high in-plane orientation, and the crystal lattice of this intermediate layer is used as a template to superconductivity. In-plane orientation and orientation of the crystal of the layer can be improved, and since it is a non-vacuum process, high-speed film formation is possible at low cost, so it is possible to manufacture a long or large area planar oxide superconducting wire. Suitable and because the crystal is biaxially oriented, it has a higher critical current density (Jc) than the Bi-based silver sheath wire, excellent magnetic field characteristics at liquid nitrogen temperature, and high critical current (Ic) value. It has the advantage that it is easy to obtain a thick film.

  Among the MOD methods described above, an organic acid salt containing fluorine (for example, TFA salt: trifluoroacetate salt) is used as a starting material, and heat treatment is performed in a steam atmosphere, so that a superconductor is obtained via decomposition of fluoride. It is preferable to use a method obtained (hereinafter referred to as TFA-MOD method). In this case, the raw material solution contains at least one of metal organic acid salts of RE, Ba and Cu containing F element, and in particular, a metal of Ba. It is preferable to use a solution in which the organic acid salt contains element F.

  For example, (i) as a metal organic acid salt solution containing RE, a solution containing any one or more of trifluoroacetate, naphthenate, octylate, levulinate, and neodecanoate containing RE, A trifluoroacetate solution containing RE, (b) a metal organic acid salt solution containing Ba as a solution of trifluoroacetate containing Ba, and (c) a metal organic acid salt solution containing Cu as a naphthenic acid containing Cu A solution containing at least one of salt, octylate, levulinate, and neodecanoate is used.

  By adopting this TFA-MOD method, a liquid phase caused by HF is formed at the interface where the superconducting film grows while generating HF gas by the reaction between the amorphous precursor containing fluorine obtained after calcining of the coating film and water vapor. In addition, the superconductor can be epitaxially grown from the substrate interface.

  In the present invention, it is preferable that the molar ratio of Ba in the REBCO-based superconductor is within a range of 1.3 <y <1.7. By making the molar ratio of Ba smaller than the standard molar ratio (2), the segregation of Ba is suppressed, and the precipitation of Ba-based impurities at the grain boundaries is suppressed, resulting in a good current path. be able to.

  The REBCO-based superconductor is laminated so that a raw material solution containing a metal element constituting the superconductor is applied on the intermediate layer and subjected to a calcining heat treatment a plurality of times so that it has a predetermined film thickness after the crystallization heat treatment. Formed.

As the substrate used in the present invention, either a biaxially oriented polycrystalline substrate or a non-oriented polycrystalline substrate can be used. As the oriented Ni substrate, RABiTS (trademark: rolling-assisted biaxially textured-substrates) in which a Ni substrate that has been cold-rolled strongly and subjected to heat treatment in a vacuum or a reducing atmosphere can be used. For example, a thin film of a liquid phase epitaxial layer of Ce ₂ Zr ₂ O ₂ and a thin film of a liquid phase epitaxial layer of CeO ₂ are sequentially formed on this oriented Ni substrate.

On the other hand, when a non-oriented polycrystalline substrate is used, an IBAD method (Ion Beam Assisted Deposition) can be used. This composite substrate using the IBAD method is formed by depositing particles generated from a target while irradiating ions from an oblique direction to a non-magnetic high-strength tape-like Ni-based substrate (Hastelloy, etc.). The intermediate layer (CeO ₂ , Y ₂ O ₃ , YSZ, etc.) that suppresses the reaction with the elements constituting the superconductor is provided, and the intermediate layer has a two-layer structure (CeO ₂ Or Y ₂ O ₃ / YSZ or Zr ₂ R _x2 O ₇ etc .: R _x represents Y, Nd, Sm, Gd, Ei, Yb, Ho, Tm, Dy, Ce, La or Er. (JP-A-4-329867, JP-A-4-33195, Japanese Patent Application No. 2000-333843).

  As the above Ni-based alloy, an alloy containing one or more elements selected from W, Mo, Cr, Fe, Cu, V, Sn and Zn in Ni can be used.

  In the present invention, since the current path is formed of an oxide superconductor having a meander shape by the MOD method, a long current path can be formed with a small cross-sectional area, and the heat intrusion path can be lengthened. Therefore, the amount of heat intrusion can be kept low, and its manufacture is easy, and it is possible to make it compact, that is, to reduce the amount of heat intrusion without changing the length of the current leads.

It is a top view which shows one Example of the current path of the meander shape used for the current lead of this invention. It is sectional drawing perpendicular | vertical to the axial direction of the oxide superconductor used for the current lead of this invention. It is a perspective view which shows one Example of the current lead of this invention.

  In the present invention, first, two intermediate layers are formed by a MOD method or a vapor phase method on a Ni—W substrate having a predetermined area (area required for physical processing described later), and on this intermediate layer. A calcined film of a REBCO superconductor is formed by the TFA-MOD method. This process is repeated a plurality of times to obtain a calcined film having a predetermined film thickness, and then a crystallization heat treatment is performed in a water vapor atmosphere to form a superconductor on the intermediate layer. In this case, it is also possible to use a composite substrate in which an intermediate layer is provided on the substrate by the IBAD method, and to form a calcined film of the REBCO superconductor on the composite substrate by the TFA-MOD method.

  Next, physical means is applied to the flat oxide superconductor formed on the substrate via the intermediate layer to create a conductor that becomes a meander-shaped current path.

  As the physical means described above, a flat oxide superconductor formed on the substrate via an intermediate layer is punched from above to punch it into a meander-shaped contour, or diamond It is possible to use either a cutting process in which a flat oxide superconductor is formed into a meander shape by a cutter or a laser processing in which a flat oxide superconductor film body is physically etched into a meander shape using a laser processing apparatus. Is possible. In this laser processing, the irradiated superconductor is decomposed or melted by irradiating a laser to the oxide superconductor to destroy the superconducting phase and transform it into a non-superconducting phase, and a current path is formed by a portion not irradiated with the laser. is there.

  The conductor serving as the meander-shaped current path is usually formed by applying physical means to the substrate after forming an oxide superconducting layer on the substrate via an intermediate layer. After forming a meander-shaped substrate, a method of forming an intermediate layer and an oxide superconducting layer thereon can be employed.

  As shown in FIG. 1, the meander-shaped current paths described above are arranged in parallel in close proximity to the connection ends 1a and 1b connected to the electrodes A and B at both ends, and formed between the connections. The odd-numbered straight line portion 2 and the connection portion 3 that sequentially connects the adjacent end portions of the straight line portion, in FIG. Examples of current paths 10 and 11 each having three straight portions are shown. In this case, the current path is mainly parallel to the direction between the electrodes A and B.

  FIG. 1C shows an example in which the current path is mainly perpendicular to the direction between the electrodes A and B. The connection ends 1a and 1b connected to the electrodes A and B at both ends, and the connection portions An odd number of straight line portions 4 that are arranged in parallel and are perpendicular to each other and perpendicular to the direction between the electrodes A and B, and a connection portion 5 that sequentially connects the adjacent ends of the straight line portions. An example of seven current paths 12 is shown.

  The above-mentioned conductor that becomes a meander-shaped current path is joined to or placed on the surface of a support member to which a pair of electrodes are connected via a low thermal conductive member made of an electrically insulating material at both ends. Accordingly, it is fixed by an insulating plate or an insulating sheet, and both ends thereof are connected to electrodes. The above current leads are entirely housed in a metal case except for the electrodes at both ends.

  As described above, by making the current path of the current lead into a meander shape, the heat intrusion path can be lengthened, the amount of heat intrusion can be remarkably suppressed, and a loop is not formed. Loss can be reduced.

  Examples of the present invention will be described below.

Example 1
As shown in FIG. 2, a composite substrate 23 in which an intermediate layer 22 composed of a Ce ₂ Zr ₂ O ₇ layer 22a and a CeO ₂ layer 22b is sequentially formed on an oriented Ni—W substrate 21 having a predetermined area is used. The raw material solution was applied onto the composite substrate and subjected to calcination heat treatment.
The Ce ₂ Zr ₂ O ₇ layer 22a, which is the first intermediate layer on the composite substrate 23, has a function as a buffer layer and suppresses a reaction with the superconducting layer to prevent a decrease in superconducting characteristics, The CeO ₂ layer 22b as the second intermediate layer is disposed in order to maintain lattice matching with the superconducting layer.
As a raw material solution, a mixed solution of Y and Ba trifluoroacetate and Cu naphthenate dissolved in 2-octanone so that Y: Ba: Cu = 1: 1.5: 3 was used.
The calcination heat treatment is performed at a maximum heating temperature of 400 ° C., and the furnace cooling from coating to heating to room temperature is repeated 10 times so that the film thickness of the superconducting layer (YBCO layer) 4 after the crystallization heat treatment becomes 1.5 μm. It was.

  Next, the calcined film on the composite substrate 23 was subjected to a crystallization heat treatment of the YBCO superconductor under a partial pressure of water vapor. This crystallization heat treatment is composed of a temperature rising process from room temperature to a maximum heat treatment temperature (crystallization heat treatment temperature) of 730 ° C., a constant temperature process at the crystallization heat treatment temperature, and a subsequent furnace cooling process to room temperature. Was kept below 50 Torr.

  On the YBCO oxide superconducting layer 24 thus formed on the composite substrate, a stabilizing layer 25 made of Ag was coated to produce a flat oxide superconductor 30. As a result of measuring the Ic value of this oxide superconductor 30, a value of 210 A / cm-width was shown.

The flat oxide superconductor 30 produced as described above was punched to form a meander-shaped current path 10 shown in FIG. The cross-sectional area of this current path was 6 × 10 ⁻⁶ , and the thermal conductivity was 43.173 W / m · K.

  14 of the meander-shaped current paths 10 are shown in FIG. 3 (in the figure, only three current paths 10 are omitted), and a low heat conduction member made of an electrically insulating material at both ends. 42 and 42 are placed on the surface of the support member 41 to which the pair of electrodes A and B are connected, and both ends 1a and 1b are connected to the electrodes A and B, respectively, and then an insulating plate and an insulating sheet (see FIG. The current lead 50 was prepared by being fixed to the support member 41 by being not shown and being housed in a metal case (not shown). In this case, the distance between the electrodes A and B is 0.2 m, and the length of the meander-shaped current path 10 is 1 m.

  The amount of heat penetration of the current lead 50 was measured at a low temperature side temperature of 20K and a high temperature side temperature of 77K under an energization current of 2000A. As a result, a value of 0.207 W / piece was shown.

Example 2
An oxide superconductor 30 was prepared in the same manner as in Example 1, and then a flat oxide superconductor was punched to form a meander-shaped current path 11 shown in FIG. The cross-sectional area of this current path was 6 × 10 ⁻⁶ , and the thermal conductivity was 43.173 W / m · K.

  Using 14 of the meander-shaped current paths 11, current leads were prepared in the same manner as in Example 1. In this case, the distance between the electrodes A and B is 0.2 m, and the length of the meander-shaped current path 11 is 0.6 m.

  As a result of measuring the amount of heat penetration of the current lead 50 at a low temperature side temperature of 20K and a high temperature side temperature of 77K under an energization current of 2000A, a value of 0.345 W / piece was shown.

Comparative Examples 1-5
A tape-shaped oxide superconductor having a cross-sectional area of 6 × 10 ⁻⁶ was prepared in the same manner as in Example 1. As a result of measuring the Ic value of this tape-shaped wire, it showed a value of 210 A / cm-width, and the thermal conductivity was 43.173 W / m · K.

  Using 14 of the tape-shaped oxide superconductors, current leads were prepared in the same manner as in Example 1. In this case, the distance between the electrodes A and B is 0.2 m, and the length of the current path is also 0.2 m.

  Table 1 shows the results of measuring the heat penetration amount of the above current leads under an energization current of 2000 A together with the low temperature side temperature and the high temperature side temperature.

Comparative Example 6
A tape-shaped oxide superconductor having a cross-sectional area of 6 × 10 ⁻⁶ was prepared in the same manner as in Comparative Example 1. As a result of measuring the Ic value of this tape-shaped wire, it showed a value of 210 A / cm-width, and the thermal conductivity was 43.173 W / m · K.

  Using 14 of the tape-shaped oxide superconductors, current leads were prepared in the same manner as in Comparative Example 1. In this case, the distance between the electrodes A and B is 0.6 m, and the length of the current path is also 0.6 m.

  As a result of measuring the heat penetration amount of the current lead under the low temperature side temperature 20K, the high temperature side temperature 77K, and the energization current 2000A, a value of 0.345 W / piece was shown.

Comparative Example 7
A tape-shaped oxide superconductor having a cross-sectional area of 6 × 10 ⁻⁶ was prepared in the same manner as in Comparative Example 1. As a result of measuring the Ic value of this tape-shaped wire, it showed a value of 210 A / cm-width, and the thermal conductivity was 43.173 W / m · K.

  Using 14 of the tape-shaped oxide superconductors, current leads were prepared in the same manner as in Comparative Example 1. In this case, the distance between the electrodes A and B is 1.0 m, and the length of the current path is 1.0 m.

  As a result of measuring the heat penetration amount of the above current lead under the low temperature side temperature 20K, the high temperature side temperature 77K, and the energization current 2000A, a value of 0.207 W / piece was shown.

  As is clear from the results of the above Examples and Comparative Examples, in the current leads (Comparative Examples 1 to 7) using the conventional tape-shaped wire, the distance between the electrodes (current path) is reduced in order to reduce the heat penetration amount. However, in the current lead according to the present invention, the current path is formed by an oxide superconductor having a meander shape formed by the MOD method. By doing so, the current lead can be made compact and its manufacture is also easy.

  The oxide superconducting current lead according to the present invention can be used as a current lead for supplying a current from a power source to a superconducting application device.

1a, 1b connecting end 2,4 straight portions 3 and 5 connecting portions 10, 11 and 12 the current path 21 oriented Ni: W substrate 22 intermediate layer 22a _Ce 2 _Zr 2 _{O 7} layer (a first intermediate layer)
22b CeO ₂ layer (second intermediate layer)
23 Composite substrate 24 YBCO oxide superconducting layer 25 Ag (stabilization layer)
30 Oxide superconducting film body 41 Support member 42 Low heat conduction member 50 made of electrically insulating material Current lead A, B Electrode

Claims (6)

  A current lead for connecting a superconducting device and a power supply source, wherein the current lead includes a pair of electrodes connected to both sides of a support member, and a current path electrically connected to the both electrodes. A current path between the electrodes is formed by a plurality of oxide superconductors having a meander shape in which an oxide superconducting layer is formed on a substrate via an intermediate layer by a MOD method, and each current path is It is arranged in close contact with or bonded to the flat support member, and each current path is connected to the both electrodes at each connection end protruding in the electrode direction at both ends thereof. Characteristic oxide superconducting current lead. A current lead for connecting a superconducting device and a power supply source, wherein the current lead includes a pair of electrodes connected to both sides of a support member, and a current path electrically connected to the both electrodes. A current path between the electrodes is formed by forming an oxide superconducting layer on the substrate by an MOD method through an intermediate layer, and adjacent to the odd-numbered linear portions arranged in parallel and adjacent to the odd-numbered linear portions. It is formed by a plurality of oxide superconductor from the connection unit for sequentially connecting the ends ing to Rutotomoni, wherein each current path is disposed in close contact or joined to on a flat of the support member, both ends The oxide superconducting current lead is connected to both electrodes at respective connection end portions projecting in the electrode direction.   3. The oxide superconducting current lead according to claim 1, wherein the current path is formed in a meander shape by applying physical means to the oxide superconductor on the flat plate. The oxide superconductor is represented by REBa _x Cu ₃ O _y (RE represents one or more elements selected from Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. X ≦ 2 and y = 6.2 to 7. Hereinafter, this is referred to as REBCO.) The oxide superconducting current lead according to any one of claims 1 to 3, which is made of a system superconductor.   5. The oxide superconducting current lead according to claim 4, wherein the REBCO-based oxide superconductor is a YBCO-based superconductor formed by a TFA-MOD method.   6. The oxide superconducting current lead according to claim 5, wherein a molar ratio of Ba is in a range of 1.3 <Ba <1.7.

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